Stable fixation of an osseointegated implant system for above-the-knee amputees: titel RSA and radiographic evaluation of migration and bone remodeling in 55 cases

Background and purpose

Rehabilitation of patients with transfemoral amputations is particularly difficult due to problems in using standard socket prostheses. We wanted to assess long-term fixation of the osseointegrated implant system (OPRA) using radiostereometric analysis (RSA) and periprosthetic bone remodeling.

Methods

51 patients with transfemoral amputations (55 implants) were enrolled in an RSA study. RSA and plain radiographs were scheduled at 6 months and at 1, 2, 5, 7, and 10 years after surgery. RSA films were analyzed using UmRSA software. Plain radiographs were graded for bone resorption, cancellization, cortical thinning, and trabecular streaming or buttressing in specifically defined zones around the implant.

Results

At 5 years, the median (SE) migration of the implant was –0.02 (0.06) mm distally. The rotational movement was 0.42 (0.32) degrees around the longitudinal axis. There was no statistically significant difference in median rotation or migration at any follow-up time. Cancellization of the cortex (plain radiographic grading) appeared in at least 1 zone in over half of the patients at 2 years. However, the prevalence of cancellization had decreased by the 5-year follow-up.

Interpretation

The RSA analysis for the OPRA system indicated stable fixation of the implant. The periprosthetic bone remodeling showed similarities with changes seen around uncemented hip stems. The OPRA system is a new and promising approach for addressing the challenges faced by patients with transfemoral amputations.The traditional method of attaching prostheses for patients who have undergone a transfemoral amputation is by means of socket prostheses. Numerous studies have documented the shortcomings of this approach (Hoaglund et al. 1983, Hagberg and Branemark 2001, Hoffman et al. 2002). Skin conditions and volume changes of the stump increase the difficulty in properly attaching and using the prosthesis (Sherman 1999, Collins et al. 2006). In addition, patients experience changes in gait, which reduces hip flexion and extension and increases pelvic tilt (Hagberg et al. 2005, Rabuffetti et al. 2005). There is also a lack of stabilization between the prosthesis and the residual limb.Brånemark introduced the concept of osseointegration in the 1950s (Sullivan 2001). Shortly afterwards, it was applied to human dental implants. Osseointegration was originally defined as “a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant” (Branemark et al. 1977, 2001). This definition has since been modified over the years as follows: “...when there is no progressive relative movement between the implant and the bone with which it has direct contact” (Branemark et al. 2001). Adell et al. (1981) maintained that the fundamental crux and success of osseointegration was threefold: a delicate surgical technique, an adequate recovery period to allow for optimal bony ingrowth, and controlled loading when use of the implant begins. The bone remodeling that occurs around an osseointegrated implant during the carefully controlled rehabilitation permits further integration of the implant into the bone and gives enhanced long-term clinical outcome. The importance of osseointegration for the long-term stability of orthopedic implants has been successfully used in total joint arthroplasty (Engh et al. 2003, Glassman et al. 2006). This approach may provide a stable and functional prosthesis for patients who cannot use a conventional socket prosthesis (Hagberg and Branemark 2009).A number of studies have examined the positive effect of osseointegrated prostheses on the skin around the site and also on joint movement relative to the effect of standard socket prostheses (Hagberg et al. 2005, Lee et al. 2007, Hagberg and Branemark 2009). Increased quality of life, overall well-being, and improved prosthetic usage have been reported (Hagberg et al. 2008).We assessed long-term fixation and stability of the osseointegrated implant using radiostereometric analysis (RSA) and periprosthetic bone remodeling on plain radiographs. Our hypothesis was that there is not substantial micromotion of the implant and that periprosthetic bone remodeling does not have a negative effect on implant stability or performance.